Means for generating involute and noninvolute gears

ABSTRACT

A machine for grinding or similarly finishing gear teeth to involute or noninvolute form has an indexable rotary worktable and a column on which is mounted a slide carrying linkage and driving mechanism for controlling and driving a grinding wheel to sweep out a tooth profile in accordance with a given kinematic equation.

United States Patent [72] inventor Peter Herbert Cleff [50] Field of Search 1. v. 51/84Q 95 5 Hartside Place, Melton Park, Gosiorth, CH, 105, 123 G, 98 Newcastle upon Tyne, N 35th. England [2|] VAppL No 93 233 [56} References Cited [22] Filed Dec. 26, 1967 UNlTED STATES PATENTS 1 Palemed M15, 1971 2,368,559 1/1945 Miller H 51/123 0 Priority Jan-@1967 2567,460 9/1951 Aeppli 51/123 0 [33] Great Britain h [31 843/67 Primary Exammer0thell M. S mpson Alt0rneyLarson, Taylor and l-lmds [54] INVOLUTE AND ABSTRACT: A machine for grinding or similarly finishing 6 Claims 6 Drawing g gear teeth to involute or noninvolute form has an indexable rotary worktable and a column on which is mounted a slide [52] U.S. Cl 1. 51/123 carrying linkage and driving mechanism for controlling and [51] Int. Cl B24b 3/00, driving a grinding wheel to sweep out a tooth profile in ac- B24b 5/00 cordance with a given kinematic equation.

, f- 2 4 I f lj 1 a 11 1 MACH/NE CUN mars GRINDING INDEX/N6 (I MA CHINE PATENTEU mu 5 I97! SHEET 1 [IF 5 MEANS FOR GENERATING INVOLUTE AND NONINVOLUTE GEARS This invention relates to means for generatively finishing, for example by grinding, the precut tooth flanks of cylindrical gear wheels or pinions having either straight spur or helical teeth of either involute, near-involute, or noninvolute form.

Although in what follows reference will be made chiefly to a grinding process, it must be clearly understood that metal removal processes such as spark-erosion, electrochemical machining and the like may be adapted to the purpose of this invention and are included within the meaning of the term grinding.

The principal object of this invention is to provide a generative gear grinding or finishing machine which is versatile and fast in operation. A second object of the invention is the provision of means whereby a rotating grinding or finishing wheel is made to carry out most, if not all, motions necessary to generate by means of its straight line generatrix, which may be constituted by a line lying in the operative transverse plane of said grinding wheel or by the external straight line conegeneratrix of a conical grinding wheel of more than I50 arcdegrees included cone angle, either true-involute or near-involute helicoids on the workgear to be ground. A third object of this invention is the provision of the basic means for the grinding of noninvolute external gears by either the straight wheel/generative" or "formed-wheel/generative" process, or internal involute gears by the latter method.

In accordance with the invention, a machine for generating the finished form of gear teeth on a work gear comprises a worktable adapted to carry said workgear and rotatable about an axis, means for step-by-step indexing of said worktable carrying said workgear about said axis, a finishing wheel having an operative part defining a generatrix to suit a given tooth form, a power-driven rotatable spindle carrying said finishing wheel, a two-part swing frame angularly movable about a pair of main pivots whose common axis is always normal to said generatrix and has a given angular relationship, in accordance with the given tooth for, to said work table axis, means for movably connecting said spindle to said swing frame so as to allow movement of said spindle and said generatrix relative to said swing frame in a plane of right angles to the common axis of said main pivots, a main swivel frame bearing said pair of main pivots, a main feed slide slidable on a main column in a direction parallel to said worktable axis, said main swivel frame being angularly adjustable and then clampable to said main feed slide, and finally means for correlating angular movement of said swing frame about said main pivots and movement of said spindle and said generatrix relative to said swing frame in such a manner that the said generatrix sweeps out as an enveloped curve said given teeth form.

One form of construction of a gear grinding machine in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a plan view of the machine, illustrating its basic components and its modus operandi in accordance with the invention,

FIG. 2 is an enlarged diagrammatic plan view of the grinding head mechanism of FIG. 1, illustrating the kinematic and mathematic principles thereof,

FIG. 3 is an enlarged diagrammatic plan view of the correlator mechanism of FIG. I, in its preferred form,

FIG. 4 shows the various forms of grinding wheel generatrix employable on a gear grinding machine in accordance with the invention,

FIG. 5 illustrates an alternative arrangement of grinding head mechanism/correlator mechanism,

FIG. 6 is a plan view of a complete grinding head mechanism/correlator mechanism combination as shown diagrammatically in FIG. 5.

GENERAL DESCRIPTION A specific description with reference to the drawings is given below but there is first given a general description which may assist understanding by readers not familiar with the subject of kinematics and the synthesis of mechanisms which the invention employs.

For the purpose of the invention, swing-frame 25 and exten sion 27 are operationally integral, once 27 has been set to the correct perpendicular radial distance from the axis of the swing-frame pivots 26. The swing-frame 25 is made to oscillate around its pivots 26 by means of a mechanism (not shown) of the lever/crank type the lever of which is represented by swing-frame 25. The amount of such oscillation is determined by the magnitude of the roll angle required for the grinding of a given work gear tooth.

A grinding spindle 28, with a drive motor 29, grinding wheel 30 and grinding wheel dressing and wear compensating device 31, is movably suspended from the extension 27 of swingframe 25 by two two-pivot links 32, 33 of equal or near equal length, respectively pivoted at 34, 35 on the grinding spindle and at 36, 37 on the extension 27 of the swing-frame 25.

On grinding spindle 28 there is provided a rectilinear guide bar 38 which is integral with said spindle and whose centerline is parallel to the (rectilinear) generatrix of grinding wheel 30.

Swing-frame 25 carries a pivot 43 at its outer end, i.e. the end away from its main pivots 26. On said pivot 43 there is rotatably held a bellcrank lever 42 with two length-adjustable arms 41 and 44. Arm 41 of bellcrank lever 42 carries at its free end a pivot 40 to which is rotatably attached a rectilinear guide bar follower 39, said guide bar follower being always in sliding contact with the aforementioned guide bar 38 integral with grinding spindle 28. The distance of pivot 40 from bellcrank lever pivot 43 is adjustable (as already mentioned) and is normally made equal to a which is equal to the setting distance of swing-frame main pivot 26 from the base cylinder of the workgear being ground, said setting distance being measured along the common normal between the axis of pivots 26 and the axis of the workgear.

The second arm 44 of bellcrank lever 42 also carries a pivot at its free end, i.e. pivot 45. Distance of pivot 45 from bellcrank lever main pivot 43 is adjustable. In addition, the perpendicular distance of the centerline of arm 44 from the bellcrank lever main pivot 43 is adjustable.

Assuming now that a finished workgear 3 is correctly positioned on worktable 2 so that a workgear tooth 4 is in the as ground" position, then in order to keep the grinding wheel generatrix in constant contact with tooth 4 and also make said generatrix cover the full radial length of said tooth, it is necessary to swing swing-frame 25 (plus extension 27) round its main pivots 26 and at the same time move the grinding wheel generatrix (if a straight line) parallel to itself in a direction towards or away from the swing-frame.

Performing the above operation as described it will easily be seen that pivot 45 will describe a curve relative to swivelframe 22, the shape of said curve being determined by the grinding wheel generatrix, by the tooth profile it is desired to grind, the distance a,,, the lengths respectively of bellcranklever arms 41 and 44; and the perpendicular offset of the centerline of arm 44 from the bellcrank lever main pivot 43.

It is the function of the correlator mechanism" to describe the resulting curve just referred to and, once pivot 45 is connected to the output member 46 of said correlator mechanism, to guide said pivot on said curve and thus establish the desired relation between swing-frame oscillation and generatrix translation relative to said swing-frame when the latter is being oscillated in the way previously described.

The correlator mechanism itself is fully illustrated in FIG. 3. It is basically of the known single crossed-slide chain" type in its most general form. As such it has, just as any other basic four-link mechanism, three external adjustments P,, P,,, and Tr, and six internal adjustments P, through P as shown and described. The correlator mechanism is driven from swingframe 25 through pivot 43 mounted thereon, through arm 44 of bellcrank lever 42 and thence through pivot 45 onto its output member 46 (FIG. I). The terms output" and input" must here be understood and applied in the correct sense; and thus 46 is output member vis-a-vis the swing-frame but input member vis-a-vis the movement of the grinding wheel generatrix relative to the swing-frame.

SPECIFIC DESCRIPTION Referring to FIG. 1 of the drawings, a machine in accordance with the invention intended to finish, e.g. by grinding, the precut tooth flanks of cylindrical gears with either spur or helical, or either true-involute, near-involute or noninvolute tooth profiles, has as a base a substantial bed I. At one end of this bed is mounted a rotary indexable worktable 2 carrying secured thereto a workgear (i.e. gear to be ground) 3 with precut teeth 4. Tooth-by-tooth indexing of this table may be carried out by means of master worm 5, driven by motor 6 through speed-change gears 7, precision clutch 8, worm shaft 9, and drive-engaging master wormwheel 10 which is integral with worktable 2, and under index control of worm shaft rotation from control box 11. Indexing may also be performed under the control of an angular (radial) diffraction grating or similar unit in coaxial drive-connection with the table spindle, in which case motor 6, speed-change gears 7, precision clutch 8, worm shaft 9, master worm and master wormwheel are merely the means for driving table and workgear into the correct angular position as determined by preset decade counters or tape-stored information.

At the other end of bed 1 there is provided a column or stanchion l2, slidably adjustable along said bed to a predetermined distance from the axis of rotation of worktable 2 plus workgear 3. Slidably mounted on this column is a feed-slide 13 which can be reciprocatingly moved by means of a feed-screw l4 journaled in column 12, and a nut 15 in engagement therewith and secured to said feed-slide. Power-drive to the feed-screw is taken from worm shaft 9 via precision clutch 16, differential l7, lead-change gears 18, line shaft 19, worm and wormwheel 21, the latter drive-connected to feed-screw 14. In this way the following essential drive combination may be obtained:

Table rotation only for setting-up and/or indexing of workgear, without moving feed-slide.

Feed-slide movement only for positioning of said feed-slide at desired height above table, without table rotation.

Table rotation and feed-slide movement together and in predetermined constant ratio one to the other, for grinding helical gears.

Located on feed-slide l3 and angularly adjustable thereagainst around an axis coplanar with, and at right angles to the table axis, is a swivel-frame 22, its location relative to 13 being controlled by spigot 23 and secured by clamping bolts 24.

A swing-frame 25 of substantially rectangular cross section is oscillatingly supported from the swivel-frame 22 by a pair of large pivots 26, the common axis of which is set to a predetermined perpendicular distance a,,+R,, from the worktable axis, in which sum 0,, is equal to the perpendicular distance of the swing-frame axis from the tangent plane to the base cylinder of the workgear and lying at right angles to the longitudinal centerline of the machine, and R, is equal to the base cylinder radius of said workgear.

Swing-frame 25 carries a right angle extension 27 whose perpendicular radial distance from the axis of pivots 26 is adjustable to permit of correct positioning radially of the grinding wheel generatrix with respect to the axis of said pivots 26. A grinding spindle 28 with drive motor 29, grinding wheel 30 and grinding wheel dressing and wear compensating device 31, is movable suspended from said extension 27 by two links 32, 33 of equal or near equal length, respectively pivoted at 34, 35 on the grinding spindle and at 36, 37 on the swingframe extension.

Integral with grinding spindle 28 and parallel to the, in this instance, rectilinear generatrix of grinding wheel 30, there is provided a straight line guide bar 38. Said guide bar is slidably engaged by a guide bar follower 39 pivotally connected at 40 to one arm 41 of a fixed angle bellcrank lever 42 pivoted at 43 on swing-frame 25, a certain predetermined radial distance away from the axis of swing-frame pivots 26. Distance 40-43 is adjustable and normally made equal to d The other arm 44 of bellcrank lever 42 and carrying a pivot 45 at its outer end, is also adjustable relative to pivot 43 both as regards length 45- 43 and the perpendicular distance of its centerline from the axis of pivot 43.

FIG. 2 illustrates more clearly than FIG. 1 the components just described in the preceding three paragraphs, and their functions, both mathematically and kinematically. FIG. 2 also demonstrates two methods of profile generation which may be employed in conjunction with a rectilinear grinding wheel generatrix, in a gear grinding machine in accordance with the invention. The first method generates the involute from its origin A on the base cylinder of radius R and using a, as the basic distance parameter; the second method generates the involute from one of its points A away from A to the same base cylinder radius R, but using a (a,,. a,,) as distance parameter.

Continuation of the description with reference now to both FIG. 1 and FIG. 3, shows pivot 45 drive-connected to the output member 46 of a correlator mechanism which essentially comprises: a baseplate 47 adjustably (P,, P,,, 11') secured to swivel-frame 22, a swinging guide block 48 pivoted on 47 by means of pivot 49, a pair of rectilinear guideways 50 adjustably secured to 47 in the direction of parameter p (parallel to coordinate axis 1 a right-angled cruciform output member 46 with centerline center 51 whose one leg 52 is pivotally connected at 53 to slide 54 which is slidable in guideways S0, and whose other leg 55 is arranged to slide through swinging guide block 48, and finally an output pivot 56 whose axis is coaxial with that of pivot 45 of bellcrank lever 42, and which can be positionally adjusted duodirectionally with respect to the centerlines of both leg 52 and leg 55 of output member 46.

Essentially the correlator mechanism shown in FIG. 1 and FIG. 3 is of the KAPPA or PAN-KAPPA-type with a total of nine independently adjustable parameters, P,, P,,, 1r p 11 1 p p,, p,;. Additional Parameters are L and A r as indicated in FIG. 2.

Extensive computer search calculations have proved the PAN-KAPPA-type of mechanism to be the optimum four-link configuration for the purposes of the invention. Other correlator mechanisms of the fourand six-link-type may be utilized, as will be readily understood by those skilled in the synthesis of such mechanisms, but they lack one significant advantage of the PAN-KAPPA configuration. This mechanism can, for instance, generate involute helicoids of any helix angle within the range of the machine with a rectilinear grinding wheel generatrix, by simply setting the swivel-frame 22 to the required helix angle and adjust the parameters of the correlator mechanism accordingly. In other words, tooth profile generation on the gear grinding machine in accordance with the invention can be carried out in a plane normal to such involute helicoids.

Owing to the versatility of the correlator mechanism just described and the special arrangement adopted for imparting to the grinding wheel generatrix an angular as well as translatory or translatory-cum-rotary movements, which latter is a principal feature of the invention, several methods for the production of tooth profiles on the workgear may usefully be employed.

Thus, using a straight line grinding wheel generatrix as illustrated in FIG. 4, A and B, true-involute, near-involute and noninvolute external helicoids may be produced. With convexly curved grinding wheel generatrix, FIG. 4, C, internal helicoids of true-involute, near-involute and noninvolute-type may be generated by what may be termed the formed wheel/generative" process. The grinding wheel generatrix shown in FIG. 4, D, which is concavely curved, may be used to advantage for the production of special external tooth profiles, also by the formed wheel/generative process.

FIGS. 5 and 6 illustrate another possible form of correlator mechanism in accordance with the invention. Swing-frame 25 pivoted at 26, right-angle extension 27, parallelogram suspended grinding spindle 28, a straight line guide bar 38 and guide bar follower 39 with pivot 40, are the same components described previously with reference to FIGS. 1, 2, 3 and 4.

The bellcrank lever 42, still pivoted on 25 by means of pivot 43, is now however different from the one previously described. lts pivot 45 at the outer end of its one arm 44 is now connected to the outer end 56 of a radius arm 57 which is pivoted on swivel-frame 22 by means of pivot 48, and whose pivot distance 57-58 is equal to the pivot distance 26-43 of the main swing-frame 25. The other arm 41 of bellcrank lever 42 has now machined into it a pair of rectilinear guideways 60 along which a slide block 59, pivoted to guide bar follower 39 by pivot 40, can be moved in timed relation to the angular oscillation of swing-frame 25.

One means of achieving such time related movements of swing-frame 25 relative to swivel-frame 22, and of slide block 59 relative to guideways 60 in arm 41 of bellcrank lever 42, is shown in FIG. 6 in the form of a fully adjustable slider-crank mechanism having adjustment parameters q 1 q and q,,. This correlator mechanism is, however, only suitable for the generation of true-involute or near-involute tooth profiles if pivot 45 is constrained to move on a circular path. If this path of pivot 45 be made noncircular, by means not shown, but easily synthesized by those skilled in the art, additional requirements as regards tooth profile generation may be met.

I claim:

1. A machine for generating the finished form of gear teeth on a workgear, comprising a worktable adapted to carry said workgear and rotatable about an axis, means for step-by-step indexing of said worktable carrying said workgear about said axis, a finishing wheel having an operative part defining a generatrix to suit a given tooth form, a power-driven rotatable spindle carrying said finishing wheel, a two-part swing frame angularly movable about a pair of main pivots whose common axis is always normal to said generatrix and has a given angular relationship, in accordance with the given tooth form, to said worktable axis, means for movably connecting said spindle to said swing frame so as to allow movement of said spindle and said generatrix relative to said swing frame in a plane at right angles to the common axis of said main pivots, a main swivel frame bearing said pair ofmain pivots, a main feed slide slidable on a main column in a direction parallel to said worktable axis, said main swivel frame being angularly adjustable and then clampable to said main feed slide, and finally means for correlating angular movement of said swing-frame about said main pivots and movement of said spindle and said generatrix relative to said swing-frame in such a manner that the said generatrix sweeps out as an enveloped curve said given tooth form.

2. A machine according to claim 1, in which said correlating means is operative in accordance with the fundamental kinematic equation: x=fla R l )=a,, sin R,,( l sin 1 wherein at is the instantaneous perpendicular distance of said generatrix from the common axis of said pair of main pivots, and is a function of the machine parameter a,,, the workgear parameter R and the independent angular variable 1 a, is the perpendicular distance between the common axis of said pair of main pivots and a base cylinder of said workgear as measured along the normal to both the common axis of said pair of main pivots and the common axis of said workgear as measured along the normal to both the common axis of said pair ofmain pivots and the common axis of said workgear and worktable;

R, is the base cylinder radius of said workgear from which the given tooth form is developed;

IS the angle of oscillation of said swing frame relative to said main swivel frame, and whose starting value and range is determined by the size of the tooth root and tooth tip roll angles of the given tooth form.

3. A machine for generating gear teeth as claimed in claim 1, in which the means for the relative movement between said spindle and said swing frame comprises a pair of links each of which is respectively pivoted on said spindle and said swing frame and whose relative active lengths determine the mode of said relative movement.

4. A machine for generating gear teeth as claimed in claim 1, in which the said swing frame is made in two parts ofwhich the first part is integral with said pair of main pivots and the second part is adjustably clampable to the first part at rightangles thereto.

5. A machine for generating gear teeth as claimed in claim 1, in which said correlating means comprises a linkmechanism.

6. A machine for generating gear teeth as claimed in claim 5, in which said correlating means comprises a substantially parallelogram linkage having a coupler link, a set of rectilinear guideways mounted on and at right angles to the centerline of said coupler link, a first slide movable in said rectilinear guideways and reciprocatingly driven by a universal slidercrank mechanism activated by the relative motion between the said swing-frame, which represents one crank of said parallelogram linkage, and said coupler link, said first slide engaging through a second slide pivoted thereon a rectilinear guide-bar mounted on said spindle parallel to said generatrix, and said generatrix being rectilinear. 

1. A machine for generating the finished form of gear teeth on a workgear, comprising a worktable adapted to carry said workgear and rotatable about an axis, means for step-by-step indexing of said worktable carrying said workgear about said axis, a finishing wheel having an operative part defining a generatrix to suit a given tooth form, a power-driven rotatable spindle carrying said finishing wheel, a two-part swing frame angularly movable about a pair of main pivots whose common axis is always normal to said generatrix and has a given angular relationship, in accordance with the gIven tooth form, to said worktable axis, means for movably connecting said spindle to said swing frame so as to allow movement of said spindle and said generatrix relative to said swing frame in a plane at right angles to the common axis of said main pivots, a main swivel frame bearing said pair of main pivots, a main feed slide slidable on a main column in a direction parallel to said worktable axis, said main swivel frame being angularly adjustable and then clampable to said main feed slide, and finally means for correlating angular movement of said swing-frame about said main pivots and movement of said spindle and said generatrix relative to said swing-frame in such a manner that the said generatrix sweeps out as an enveloped curve said given tooth form.
 2. A machine according to claim 1, in which said correlating means is operative in accordance with the fundamental kinematic equation: x f(ao, Ro, phi ) ao sin phi -Ro( phi -sin phi ), wherein x is the instantaneous perpendicular distance of said generatrix from the common axis of said pair of main pivots, and is a function of the machine parameter ao, the workgear parameter Ro and the independent angular variable phi ; ao is the perpendicular distance between the common axis of said pair of main pivots and a base cylinder of said workgear as measured along the normal to both the common axis of said pair of main pivots and the common axis of said workgear as measured along the normal to both the common axis of said pair of main pivots and the common axis of said workgear and worktable; Ro is the base cylinder radius of said workgear from which the given tooth form is developed; phi is the angle of oscillation of said swing frame relative to said main swivel frame, and whose starting value and range is determined by the size of the tooth root and tooth tip roll angles of the given tooth form.
 3. A machine for generating gear teeth as claimed in claim 1, in which the means for the relative movement between said spindle and said swing frame comprises a pair of links each of which is respectively pivoted on said spindle and said swing frame and whose relative active lengths determine the mode of said relative movement.
 4. A machine for generating gear teeth as claimed in claim 1, in which the said swing frame is made in two parts of which the first part is integral with said pair of main pivots and the second part is adjustably clampable to the first part at right-angles thereto.
 5. A machine for generating gear teeth as claimed in claim 1, in which said correlating means comprises a link-mechanism.
 6. A machine for generating gear teeth as claimed in claim 5, in which said correlating means comprises a substantially parallelogram linkage having a coupler link, a set of rectilinear guideways mounted on and at right angles to the centerline of said coupler link, a first slide movable in said rectilinear guideways and reciprocatingly driven by a universal slider-crank mechanism activated by the relative motion between the said swing-frame, which represents one crank of said parallelogram linkage, and said coupler link, said first slide engaging through a second slide pivoted thereon a rectilinear guide-bar mounted on said spindle parallel to said generatrix, and said generatrix being rectilinear. 